Sangkook Choi

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The origin of magnetic flux noise in superconducting quantum interference devices with a power spectrum scaling as 1/f (f is frequency) has been a puzzle for over 20 years. This noise limits the decoherence time of superconducting qubits. A consensus has emerged that the noise arises from fluctuating spins of localized electrons with an areal density of(More)
Relativistic quantum mechanics predicts that when the charge of a superheavy atomic nucleus surpasses a certain threshold, the resulting strong Coulomb field causes an unusual atomic collapse state; this state exhibits an electron wave function component that falls toward the nucleus, as well as a positron component that escapes to infinity. In graphene,(More)
Optical absorption is the most fundamental optical property characterizing light-matter interactions in materials and can be most readily compared with theoretical predictions. However, determination of optical absorption cross-section of individual nanostructures is experimentally challenging due to the small extinction signal using conventional(More)
The sensitive structural dependence of the optical properties of single-walled carbon nanotubes, which are dominated by excitons and tunable by changing diameter and chirality, makes them excellent candidates for optical devices. Because of strong many-electron interaction effects, the detailed dependence of the optical oscillator strength f(s) of excitons(More)
We conducted micromagnetic numerical studies on the strong radiation of spin waves (SWs) produced by the magnetic-field-induced reversal of a magnetic vortex core, as well as their wave behaviors in magnetic nanowires. It was found that the radial SWs can be emitted intensively from a vortex core in a circular dot by virtue of localized large torques(More)
Electron supercollimation, in which a wave packet is guided to move undistorted along a selected direction, is a highly desirable property that has yet to be realized experimentally. Disorder in general is expected to inhibit supercollimation. Here we report a counterintuitive phenomenon of electron supercollimation by disorder in graphene and related Dirac(More)
Submitted for the MAR10 Meeting of The American Physical Society Localization of Metal-Induced Gap States at the Metal-Insulator Interface: Origin of Flux Noise in SQUIDs and Superconducting Qubits SANGKOOK CHOI, DUNG-HAI LEE, STEVEN G. LOUIE, JOHN CLARKE, University of California at Berkeley and Lawrence Berkeley National Lab — The origin of magnetic flux(More)
Vacancy-induced magnetism in graphene bilayers is investigated using spin-polarized density functional theory calculations. One of two graphene layers has a monovacancy. Two atomic configurations for bilayers are considered with respect to the position of the monovacancy. We find that spin magnetic moments localized at the vacancy site decrease by ∼10% for(More)
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